Skin conductance is known as a measure for short-term effective reactions, such as emotions. In this sense, skin conductance is typically analyzed using the phasic component of the skin conductance signal, having rises and falls of duration in the order of seconds.
For example the article “Effect of movements on the electrodermal response after a startle event” by J. Schumm, M. Bachlin, C. Setz, B. Arnrich, D. Roggen and G. Tröster, Second International Conference on Pervasive Computing Technologies for Healthcare, 2008, pages 315-318, discloses an electrodermal activity (EDA) sensor that measures the EDA at the fingers via finger straps, performs signal processing of the EDA and simultaneously measures the acceleration of the fingers. The effect of continuous, stationary movements on the EDA is presented. Controlled speeds of walking as movements and startle events as an actuator are performed. The EDA is investigated by measuring the conductivity of the skin. The signal consists of a tonic component and a fast-changing phasic component superposed on the tonic component. The startle event leads to peak-shaped responses in the phasic part of the signal. A simple peak-detection algorithm with a threshold is applied to the phasic signal. A similar device is also described in the article “Discriminating Stress From Cognitive Load Using a Wearable EDA Device” by C. Setz, B. Arnich, J. Schumm, R. La Marca, G. Tröster, U. Ehlert, IEEE Transactions on Information Technology in Biomedicine, Vol. 14, No. 2, March 2010, pages 410-417.
When considering the determination of a stress level from a physiological signal, it is important to discriminate between short-term stress and long-term stress. Short-term stress is usually conceptualized in terms of startle responses or events, i.e. the user faces a changed context and the user's body acts quickly to adapt to the new context situation, resulting in a change of a physiological signal. Long-term stress occurs when short-term stress happens too often, without sufficient possibility to recover from it. The effects build up, causing more bodily processes to change or be disturbed, resulting possibly in illnesses because of a weaker immune system, burn-out syndrome and the like.
For example, in “Central effects of stress hormones in health and disease: Understanding the protective and damaging effects of stress and mediators”, B. McEwen, European Journal on Pharmacology 583, 2008, pages 174-185, it is disclosed that, on the one hand, acute stress (short-term) responses promote adaptation and survival via responses of neural, cardiovascular, autonomic, immune and metabolic systems, and, on the other hand, chronic (long-term) stress can promote and exacerbate pathophysiology through the same systems that are dysregulated. The burden of chronic (long-term) stress and accompanying changes in personal behaviors is called allostatic overload.
The general problem with physiological signals is a good interpretation of these signals. Generally, the context situation in which the physiological signal was measured must be known.